The present invention relates generally to containers formed of thermoplastic material and methods of fabricating such containers. More particularly, the present invention relates to plastic trash containers of the type adapted for mechanized emptying by an automated dumping apparatus of the semi-automatic type and to methods of blow molding such containers.
In recent years, municipalities as well as private firms have increasingly begun to implement and utilize automated trash collection systems for curb side trash collection to obtain the advantages of increased trash collection speed, a corresponding reduction in required equipment and personnel, and an attendant reduction in required manual handling of trash containers, all of which ultimately result in significant savings in the overall costs of operation of a trash collection system. Basically, most automated trash collection systems involve the use of an automated dumping apparatus mounted on a collection vehicle for mechanized lifting and inversion of compatible trash containers to empty their contents into the collection vehicle. In so-called semi-automatic trash collection systems, special trash containers are utilized each having an upper and lower lifter bar by which the container may be mounted by collection personnel onto a compatible automated dumping apparatus on the collection vehicle for mechanized inversion of the trash container by its lifter bars to empty its contents into the collection vehicle. Representative examples of trash containers of this semi-automatic type are the various models of ROLL-A-WASTE.RTM. plastic containers manufactured and sold by Zarn, Inc., of Reidsville, N.C., the assignee hereof. Representive examples of compatible semi-automatic dumping apparatus are the TUCK-AWAY.RTM. brand dumping unit manufactured and sold by Perkins Manufacturing Company, of Le Grange, Ill. and the dumping apparatus disclosed in Wyman et al U.S. Pat. No. 4,479,751.
Conventionally, the main container body of such semi-automatic trash containers is fabricated of a plastic material such as high density polyethylene which provides suitable strength, durability and corrosion resistance for long-term usage. Of the various conventional methods by which such plastic containers can be fabricated, blow molding is considered advantageous over thermoforming and rotational molding techniques in providing superior stress and crack resistance, impact strength and useful life. On the other hand, the lifter bar components of conventional semi-automatic trash containers are typically formed of tubular metal and bolted to the exterior of the main container body, which is conventionally thought to be necessary, or to be at least the most economical manner, to achieve the three-fold criteria of properly configuring the lifter bars to be compatible with conventional semi-automatic dumping apparatus, providing sufficient strength of joinder of the lifter bars to the container body to withstand the forces typically exerted on the trash containers by such dumping apparatus, and also enabling the container bodies to be shipped in a nested fashion with other like containers. Disadvantageously, however, such metal lifter bars require special treating of the metal surfaces to provide suitable corrosion resistance and further require a separate assembly step in bolting the bars to the container body, all of which adds to the overall cost of the container. It would be significantly more desirable to utilize lifter bars fabricated of the same plastic material as the main container body and to bond the lifter bars to the container body as part of the molding process, if the above-mentioned three-fold criteria of dumpercompatible lifter bar configuration, secure lifter bar affixation to the container body, and nestability of the containers could be reasonably achieved economically.